Ion implantation is a process of depositing chemical species into a substrate by direct bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used primarily for doping processes that alter the type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is often crucial for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energy levels.
FIG. 1 depicts a conventional ion implanter system 100. The ion implanter 100 includes a power source 101, an ion source 102, extraction electrodes 104, a 90° magnet analyzer 106, a first deceleration (D1) stage 108, a 70° magnet analyzer 110, and a second deceleration (D2) stage 112. The D1 and D2 deceleration stages (also known as “deceleration lenses”) are each comprised of multiple electrodes with a defined aperture to allow an ion beam to pass therethrough. By applying different combinations of voltage potentials to the multiple electrodes, the D1 and D2 deceleration lenses may manipulate ion energies and cause the ion beam to hit a target workpiece 114 at a desired energy. A number of measurement devices 116 (e.g., a dose control Faraday cup, a traveling Faraday cup, or a setup Faraday cup) may be used to monitor and control the ion beam conditions.
It has been discovered that a relatively low wafer temperature during ion implantation improves implantation performance. Although low-temperature ion implantation has been attempted, conventional approaches suffer from a number of deficiencies. For example, low-temperature ion implantation techniques have been developed for batch-wafer ion implanters, while the current trend in the semiconductor industry favors single-wafer ion implanters. Batch-wafer ion implanters typically process multiple wafers (e.g., batches) housed in a single vacuum chamber. The simultaneous presence of several chilled wafers in the same vacuum chamber, often for an extended period of time, requires extraordinary in-situ cooling capability. Pre-chilling an entire batch of wafers is not an easy option since each wafer may experience a different temperature increase while waiting for its turn to be implanted. In addition, extended exposure of the vacuum chamber to low-temperature wafers may result in icing from residual moisture.
Also, almost all existing low-temperature ion implanters cool wafers directly during ion implantation. Apart from causing icing problems in a process chamber, direct cooling requires incorporation of cooling components (e.g., coolant pipelines, heat pumps, and additional electrical wirings) into a wafer platen itself. In general, modern wafer platens are already fairly sophisticated and highly optimized for room-temperature processing. As a result, modification of an existing ion implanter or designing a new ion implanter to accommodate low-temperature processes may be complicated and may have unwanted impacts on the ion implanter's ability to perform room temperature ion implantation processes.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current technologies for changing temperature of a platen.